#include<stdio.h>
#include<math.h>

int main()
{
	int n;
	double m,sum=0,sign=1;
	scanf("%d",&n);
	for(;sign<=n;sign++){
		m=pow(-1,sign-1)*sign/(2*sign-1);
		sum+=m;
	}
	printf("%.3lf",sum);
	return 0;
}
